Flooring adhesives are employed for adhesively bonding carpets, plastic floor coverings, made from PVC or polyolefin, for example, and for adhesively bonding coverings made from natural substances such as cork or wood. Floor covering adhesives used are predominantly dispersions based on acrylate polymers. These dispersions are especially suitable for application as floor covering adhesives because the low glass transition temperature of the acrylate polymers, customarily based on butyl acrylate and/or 2-ethylhexyl acrylate, give the polymer films a high surface tack.
On an alkaline substrate at a pH>9.0, however, acrylate-containing dispersions release the corresponding volatile alcohols through hydrolysis of the ester group. Thus butyl acrylate releases butanol and 2-ethylhexyl acrylate releases 2-ethylhexanol, which may be emitted to the ambient air. Accordingly, flooring adhesives based on vinyl acetate-ethylene copolymers have been developed.
EP 0 699 692 A2 discloses polymers of vinyl acetate, ethylene, and (meth)acrylic ester which are grafted with cellulose ether and which are recommended as flooring adhesives. A disadvantage here is that these copolymers still always have a high fraction of OH-acrylic ester monomer units and/or (meth)acrylic ester monomer units and are therefore unsatisfactory in terms of VOC emissions.
Copolymers of this kind with a high fraction of OH-acrylic ester monomer units, in use as heat-resistance pressure-sensitive adhesives, are also described in EP 0 216 210 A1.
From EP 0 699 691 A1 it is known that the adhesive qualities of aqueous dispersions of vinyl acetate-ethylene copolymers can be improved by modifying the dispersion with fully hydrolyzed polyvinyl alcohol, in other words with a polyvinyl alcohol having a degree of hydrolysis of more than 90 mol %. A problem here is the compatibility of vinyl acetate-ethylene copolymer dispersions comprising partially hydrolyzed polyvinyl alcohol with such highly hydrolyzed polyvinyl alcohols. To improve the compatibility it is proposed that a mixture be used of partially hydrolyzed polyvinyl alcohols in order to stabilize the vinyl acetate-ethylene copolymer dispersion.
EP 1 069 169 A1 proposes improving the tradeoff between VOC emissions and adhesive properties by copolymerizing, rather than (meth)acrylic ester comonomers, vinyl esters of alpha-branched carboxylic acids (vinyl esters of Versatic acid, such as VeoVa9 or VeoVa10 from Momentive). Even vinyl esters of this kind, however, are subject to the hydrolysis, and Versatic acid that is released, in analogy to hydroxycarboxylic acids released by hydrolysis, leads to unpleasant odor in application as bonding agents.
EP 0 530 013 A1 describes bonding agents based on vinyl acetate-ethylene copolymers, the copolymer recommended for flooring adhesives being obtained by copolymerization of 5 to 85 wt % of vinyl acetate, 10 to 50% of ethylene, and 5 to 85 wt % of a high vinyl esters such as vinyl 2-ethylhexanoate. Disadvantages are the high costs due to the high fractions of higher vinyl esters, and the prolonged polymerization time on copolymerization of large amounts of higher vinyl esters.